If the originals are white powder coat from the factory and the black is spray paint,try oven cleaner. Easy Off oven cleaner is known in the classic car world to remove paint. Spray it on, leave it sit for a few, rub off with a rag. Don't leave it too long if you're trying to preserve the factory layer. This method of paint removal is all about trial and error. If you have to respray them in the end, you have nothing to lose by giving it a shot. I used it on 80's lacquer paint on my '66 VW's dash. Worked perfectly but it's slow. Just take your time and be patient.